Prediction of life durability in friction for wet clutches of DCT gearboxes

Abstract: Many new cars are equipped with automatic transmissions. These gearboxes often have a dual clutch transmission (DCT) that has a built-in wet clutch. The lubricants used in these gearboxes is often very advanced because it must take care of two systems, the wet clutch and the gears. There is always a strive to make the drain intervals longer. To do this a fundamental understanding of the aging mechanisms inside a DCT must be understood. This project focuses at the aging of the lubricant and friction material inside the wet clutch. A test rig at Luleå University of Technology is redesigned to be able to age this kind of systems. The test rig contains a wet clutch from Volvo Construction Equipment and the redesign focuses mainly on decreasing the oil sump volume to 6 liter and getting the oil sump to be at 100 °C during the tests. To verify the test rig a test is done that are trying to mimic a test done on a test rig called ZF GK3. The same lubricant, friction material and grove pattern are used as in the test with the ZF GK3. Due to the difference in how the test rigs are built all parameters cannot be held the same during the test. At first the same sliding speed at the mean radius, the average power over an engagement and the oil sump temperature is kept the same. A drop in the static friction can then be seen over time. This was however not the expected behavior. The sliding speed is therefore increased which also increases the average power and transferred energy per engagement. This has also big effects on the temperature inside the clutch. A drop in the coefficient of friction can then be seen at 50 % of the sliding speed which also is seen on the test carried out on the ZF GK3. This verifies that the test rig can be used for aging of these kind of systems.The aging that takes place seems to be dependent on the temperature inside the clutch.